1. Field of the Invention
This invention relates to method and a particle cooler for controlling the cooling effect in a circulating fluidized bed reactor. The bed circulates through a reaction chamber, particle separator and a particle flow restrictor with fluidizing means.
2. Description of the Prior Art
Particle coolers of the above type are known, e.g. from European Patent Application EP No. 0093063 corresponding to U.S. Pat. No. 4,552,203, and are used to control the output of heat within the loop of reaction chamber--particle separator--reaction chamber, and/or regulation of operating temperature within the reaction chamber.
In known adjustable particle coolers, the particle flow coming from separators is divided into two separate streams; one stream is returned directly to the reaction chamber, and the other stream is led to the particle cooler. This splitting of the particle stream requires investments in the form of conduits and valves. One problem with known arrangements having divided particle steams, is dimensioning the size of the particle cooler. If the particle cooler is dimensioned for a small reduction of temperature in the particle stream (mixing temperature) at full heat output from the cooler, then a reduction in particle flow, e.g. when the load is reduced, will result in an initially increased reduction of temperature in the particle flow, but the heat output in the particle cooler will hardly be affected. The reduction in output will only be obtained after a substantial reduction in temperature difference (T.sub.particle -T.sub.coolant media). In order to avoid this control deficiency, the particle cooler may be dimensioned for a larger reduction of temperature in the particle stream, i.e. only a minor part of the total particle flow will be led through the particle cooler, even at full load. This leads to a better adjustability. However, one drawback is that a larger cooling surface is needed to compensate for the reduced driving temperature difference.